1. Field of the Invention
The present invention relates to an image forming apparatus and a control method for the same. More specifically, the invention relates to an image forming apparatus having a function of adjusting an image formation condition according to a change with time or an environmental change, and a control method for the same.
2. Related Background Art
Up to now, image forming apparatuses adopting an electrophotographic system etc., such as a printer and a copying machine perform image formation as follows. That is, a surface of a uniformly charged image bearing member is exposed to light by an exposing apparatus to form an electrostatic latent image. The electrostatic latent image on the image bearing member is developed with a toner to form a toner image. The toner image is transferred from the image bearing member onto a recording material such as recording paper. The toner image on the recording material is then applied with heat and pressure and fixed onto the recording material.
Here, each process for the image formation is appropriately controlled by control means provided inside the image forming apparatus and having a processor and input/output terminals for a signal.
A case of forming a multi-color image with the above image forming apparatus is assumed. A high voltage unit is provided in the apparatus, which is for applying a developing bias to a developing unit for developing the electrostatic latent image and a transfer bias to a transfer-charger according to the number of times the image is transferred in respective colors. The control means turns ON/OFF the high voltage unit in turn according to image formation cycles in multiple colors, thereby forming the multi-color image.
FIG. 8 is a block diagram illustrative of a printer control mechanism of the printer as the image forming apparatus.
In FIG. 8, reference numeral 3 denotes a video signal; 4, a driving circuit; 5, a laser driving signal; 6, an activation signal; 7, a bias control means; 8, a bias signal for transferring, developing, etc.; 18; a video interface; 20, a control unit; 52, a printing sequence signal; 54, a printing means; 55, an actuator driving signal; 81, a notification means; 83, a printing sequence control means; 100, a printer control circuit; 110, a printer controller; 120, a printer engine; 121, an exposing apparatus; 122; a high voltage unit; and 123, a conveyance means etc.
As shown in FIG. 8, the printer control circuit 100 is electrically connected with the printer controller 110 for processing image data etc. or processing internal information of the printer etc.
At the time of forming the image, a multi-color image signal is transmitted from the printer controller 110 to the printer control circuit 100. The control unit 20 provided inside the printer control circuit 100 then generates the video signal 3 according to the transmitted image signal and outputs the signal to the driving circuit 4.
The driving circuit 4 is used for driving a semiconductor laser and allowed to output the laser driving signal 5 to the exposing apparatus 121.
Also, the printing means 54 connected to the control unit 20 outputs the actuator driving signal 55 for driving actuators such as a motor, a clutch, and a solenoid, according to the printing sequence signal 52 from the control unit 20 or sensor information, thereby actuating the conveyance means etc. 123 for conveying the recording paper.
The control unit 20 outputs a first video signal and a second video signal generated according to the multi-color image signal via the driving circuit 4 to form a first electrostatic latent image and a second electrostatic latent image on the image bearing member (not shown). At the same time, the control unit outputs the activation signal 6 to the bias control means 7.
In response to the activation signal, the bias control means 7 outputs the bias signal 8 to the high voltage unit 122 used for a transfer or development operation according to the activation signal, with which the electrostatic latent image is developed and the toner image is transferred onto the recording paper. Thus, the multi-color image can be formed.
Further, the printing sequence control means 83 connected to the control unit 20 sends to the control unit 20 a printing sequence for processing accompanied with the detection of information on an open/close state of a printer cover or for a normal print operation.
Also, the notification means 81 connected to the control unit 20 notifies the printer controller 110 of the information of the printer engine 120 at the image formation time as a status, via the video interface 18 connecting between the printer control circuit 100 and the printer controller 110.
Next, referring to FIGS. 9 and 10, signals of the video interface 18 are described.
FIGS. 9 and 10 show the signals of the video interface in detail.
In particular, FIG. 9 shows typical signals transferred between the printer controller 110 and the printer control circuit 100.
In the figures, symbol “/” prefixed to an abbreviation code for each signal name means that the signal is a negative logic signal.
Printer power ready signal “/PPRDY”: a signal indicating that a printer apparatus is ready to communicate after being initialized etc. through power-on. The signal is transmitted from the printer control circuit 100 to the printer controller 110.
Controller power ready signal “/CPRDY”: a signal indicating that the printer controller 110 is ready to communicate after being initialized etc. through power-on. The signal is transmitted from the printer controller 110 to the printer control circuit 100.
Ready signal “/RDY”: a signal indicating that a print operation is allowed to start in response to a signal “/PRNT” requesting the apparatus to start the print operation as described below. The signal is transmitted from the printer control circuit 100 to the printer controller 110. This signal can be set to “truth” with the proviso that each portion of the printer normally operates, for example, an inner temperature of a fixing apparatus reaches a predetermined temperature; no recording paper remains inside the printer; or a polygon mirror rotates at a given speed.
Print signal “/PRNT”: the signal requesting the apparatus to start or continue the print operation. The signal is transmitted from the printer controller 110 to the printer control circuit 100.
Top of page signal “/TOP”: a synchronization signal as a reference for vertical scanning of the image. The signal is output from the printer control circuit 100 a certain time period after the signal “/PRNT” is output from the printer controller 110.
Line synchronization signal “/LSYNC”: a synchronization signal as a reference for horizontal scanning of the image. The signal is, similarly to the signal “/TOP”, output from the printer control circuit 100 a certain time period after the signal “/PRNT” is output from the printer controller 110.
Video clock signal “/VCLK”: a synchronous clock synchronized with signals “/VDOEN” and “/VDO” described below. The signal is generated by the printer controller 110.
Image enable signal “/VDOEN”: a signal for inputting the image signal “/VDO” output from the printer controller 110 to the printer control circuit 100. The printer control circuit 100 detects whether the signal “/VDOEN” is set to truth or false in synchronization with the signal “/VCLK”, and inputs the image signal “/VDO” in the case of truth but does not input the image signal “/VDO” in the case of false.
Image signal “/VDO”: image data output from the printer controller 110 and synchronized with the signal “/VCLK” with the signal “/TOP” as a reference (in a vertical direction of the image) and with the signal “LSYNC” as a reference (in a horizontal direction thereof). Thus, the signal “/VDO” is output.
Controller clock signal “/CCLK”: a command serial-transferred from the printer controller 110 to the printer control circuit 100 and a synchronous clock for a status serial-transferred to the printer controller 110 from the printer control circuit 100. The signal is output from the printer controller 110.
Command signal “/CMD”: a signal used for the printer controller 110 to serial-transfer the information to the printer control circuit 100, the information being called the “command”.
Command busy signal “/CBSY”: a signal indicating to the printer control circuit 100 that the printer controller 110 serial-transfers the command using the signal “/CMD”.
Status signal “/STS”: a signal used for the printer control circuit 100 to serial-transfer the information to the printer controller 110, the information being called the “status”.
Status busy “/SBSY”: a signal indicating to the printer controller 110 that the printer control circuit 100 serial-transfers the status using the signal “/STS”.
Condition change notification “/CCRT”: a signal for notifying the printer controller 110 that the status inside the printer changes. The printer controller 110 issues, after receiving the signal, the command for inquiring of the printer control circuit 100 which condition is changed on the printer engine 120 side, using the signal “/CMD”. The printer control circuit 100 replies to the command using the signal “/STS”.
The signal “/CCRT” is inverted to truth when any change occurs in the printer condition previously designated by the printer controller 110.
Other signals such as speed change “/SPCHG”, paper delivery “/PDLV”, and top of paper “/TOPR” are also cited.
Next, referring to FIG. 11, a timing of each signal at the time of using the signal “/CCRT” is described.
FIG. 11 is a timing chart showing an example of a timing of each signal at the time of using the signal “/CCRT”.
FIG. 11 shows a case where the signal “CCRT” is set to truth when the printer controller 110 sends the signal “/CMD” indicating “no sheet”, for instance.
In this case, for example, if only one recording sheet remains in a recording paper cassette but the printer controller 110 makes a request that two sheets are printed, the first sheet may be printed without fail; however, at the beginning of the image formation for the second sheet, the printer control circuit 100 detects the condition change, i.e., “no sheet” and changes the signal “/CCRT” from false to truth as shown in FIG. 11.
As soon as the printer controller 110 detects that the signal “/CCRT” is changed to truth, the controller performs the following operation in order to ascertain which feeding cassette comes into the condition of “no sheet”. That is, as shown in FIG. 11, the controller changes the signal “/CBSY” to truth and issues the command that requests the printer control circuit 100 to send the status indicating whether or not the recording paper remains in the feeding cassette using the signal “/CMD”. As shown in FIG. 11, in response to the command, the printer control circuit 100 changes the signal “/SBSY” to truth and sends the status indicating whether or not the recording paper remains in the recording paper cassette using the signal “/STS”.
Note that, the state of the signal “/CCRT” is cleared to false at a timing where the signal “/SBSY” is changed to truth, which indicates that the status is transferred.
Next, referring to FIG. 12, the transfer of the command/status between the printer controller 110 and the printer control circuit 100 is described.
FIG. 12 is a sequence chart showing a transfer example of the command/status between the printer controller 110 and the printer control circuit 100 on the assumption that a color image is formed.
When the printer is instructed to start the print operation, the printer controller 110 performs image processing etc. while issuing a command to the printer control circuit 100 to check whether or not the printer is in a ready condition.
Subsequently, the controller issues a command to designate the feeding cassette and further, a command to request a desired size of the recording paper received in the designated feeding cassette.
Next, the printer controller 110 issues a command to designate a desired discharge port, a page mode designation command to designate a desired number of pages for image formation, and a command to designate either monochrome or color image formation. Thus, the designation is completed for all items.
The printer control circuit 100 replies to a series of commands and sends the corresponding status.
After that, the printer controller 110 generates the signal “/PRNT”. In response to the signal, the printer control circuit 100 returns the signal “/TOP” after a predetermined time period.
The signal “/VDO” synchronous with the signal “/TOP” in the vertical scanning and with the signal “/LSYNC” in the horizontal scanning is synchronized with the signal “/VCLK” and transferred to the printer control circuit 100.
Note that if the color mode is set, the signal “/TOP” requests the printer to start forming an image for each color component. Therefore, if the signal “/TOP” is generated four times, the image in four colors C, M, Y, and K can be formed.
After the final signal “/TOP” is generated, the printer controller 110 restores the signal “/PRNT” to false.
From the above, the printer control circuit 100 detects that the requested print operation is completed. The processing is shifted to post-processing such as cleaning of each portion.
On the other hand, the recording paper onto which the toner image is transferred is discharged from the designated discharge port after passing through a fixing roller.
Finally, the printer controller 110 confirms, based on the status sent from the printer control circuit 100 that the conveyance (discharge) of the recording paper is completed.
When the discharge completion is confirmed, a print job is finished, allowing the printer controller 110 to wait for a next print request in a ready condition.
During the above print operation, if illegal conditions occur, for example, the recording paper is jammed or used up, or users open the printer apparatus cover, the printer control circuit 100 immediately notifies the printer controller 110 that the printer is in an abnormal condition using the signal “/CCRT”.
Then, the printer controller 110 identifies the generated abnormality from the status sent in response to the command and conducts the processing according to the abnormality.
In the above printer engine 120, in particular, printer engine for outputting the color image, a density of an output image or a density balance is gradually varied along with an increase in the number of output sheets or according to an environmental change, although the variation is not suddenly caused.
Similarly, regarding a color misregistration of the formed image, a phase shift of a developing drum, or the like, the conditions for the image formation are not always optimum depending on whether or not the user exchanges the cartridge, the environmental change, the change with time, or other factors.
Thus, by monitoring whether or not the cartridge is exchanged, the elapsed time, the number of output sheets, and the environmental change, those conditions for the image formation are adjusted to optimum ones (see Japanese Patent Application Laid-Open No. 2002-29092, for example).
Hereinafter, the sequence of judging whether to execute those adjustments or not by the printer engine 120 and the printer controller 110 is explained while focusing on a density control by way of example.
The printer engine 120 capable of outputting the color image cannot output an appropriate image particularly at the time of forming the color image, unless the color components Y, M, C, and K used for the image formation are well-balanced in density.
The reason the density balance is lost is that a residual charge of a photosensitive member increases due to the repetitive image formation or that a humidity and a temperature of the environment surrounding the apparatus are changed, for instance. Under the conditions in an initial application range, the appropriate image formation cannot be performed.
To cope therewith, a change of some factors whereby the density balance is lost is detected to make a control for keeping densities in balance.
Examples of the factor as a detection target include: factors “continuous rest time in a stand-by condition”, “the number of discharged recording sheets” (hereinafter, referred to as “accumulated sheets number” in some cases), and “the number of images formed on an intermediate transfer member” (hereinafter, referred to as “accumulated images number” in some cases), all of which are detected by a CPU (not shown) mounted to the printer control circuit 100; and a change in temperature or humidity detected by the CPU (in the printer control circuit 100) monitoring the input from an environmental sensor disposed inside the printer apparatus.
Next, referring to FIG. 13, a judgement of whether to control the density or not by the printer control circuit 100 is explained.
FIG. 13 is a flowchart showing a control sequence for judging whether to control the density or not by the printer control circuit 100. The CPU in the printer control circuit 100 executes the sequence, which always monitors the change of the factors as the detection target.
In step S161, judgement is made of whether or not the accumulated sheets number/accumulated images number reached a predetermined value at which the density control execution was necessary; in step S162, judgement is made of whether or not the continuous rest time reached a predetermined value at which the density control execution was necessary. In step S163, the judgement is made of whether or not the change in environmental condition such as a temperature or a humidity reached the level at which the density control execution was necessary.
If it is judged that the density control is necessary, the printer control circuit 100 notifies the printer controller 110 that it is necessary to execute the density control using the signals “/CCRT” and “/STS” (step S164).
Next, in step S165, the printer control circuit waits for an instruction to execute the density control from the printer controller 110 and starts the density control in step S166 immediately after receiving the instruction.
In general, employed are the plural factors whereby the judgement is made of whether to perform various adjustments or not. In some cases, the factors are classified into two types: a factor whereby the adjustment is judged indispensable in order to meet a specification regarding the output image quality; and a factor whereby the adjustment is optionally judged necessary for the purpose of setting the optimum image formation conditions at the time to further improve the output image quality.
Meanwhile, as exemplified above, the judgement is made of whether to execute the various adjustments or not inside the printer control circuit. Thus, the printer controller 110 cannot guess which factor suggests the necessity of the adjustment.
Therefore, when the printer control circuit 100 notifies the printer controller 110 that it is necessary to execute the adjustment according to the above sequence, the printer controller 110 instructs the printer control circuit to execute the necessary adjustment without fail.
In general, the execution sequence of the adjustments requires several tens of seconds to several minutes, during which the user cannot obtain a print output.
As a result, the adjustment sequence is executed, which is unnecessary for the user who demands a high image output speed or response speed rather than the high output image quality.